The present invention relates to communications networks, and more particularly to controlling parameters of connections to be set up within such networks.
The term “connection” is used herein to mean a communications link defined by a connection path passing via an ordered sequence of network elements defining nodes, such as, for example, switches or routers.
As the person skilled in the art knows, a connection is generally defined, in addition to its connection path, by parameters having values that must lie within predefined ranges as a function of a service level agreement (SLA) between its user(s) and the network operator.
So long as the parameters of a connection remain within their respective ranges, the agreement is being complied with.
Nevertheless, in certain situations, a user may desire that one or more of the parameters of the connection that is to be used should not exceed a maximum value equal to the top limit of its predefined range. Such an option is made available in certain communications networks, such as those known as label switched networks, e.g. of the multiprotocol label switching (MPLS) type or the generalized MPLS (GMPLS) type.
More precisely, in networks of the above-specified type and in the context of the layer-2 label switched path (L2 LSP) type, proposals have been made to integrate each maximum value in an attribute, referred to as “SENDER_TSPEC”, in the connection setup message that is transmitted from one node to another along a connection path. That type of integration is described in particular in the document “Generalized MPLS (GMPLS) RSVP-TE signaling in support of layer-2 label switched paths (L2 LSP)”, by P. Papadimitriou et al., that is available on the Internet at the address http://www.ietf.org/internet-drafts/draft-papadimitriou-ccamp-gmpls-12sc-lsp-02.txt.
Each network element defining a node on the connection path is arranged in such a manner as to verify whether it can individually satisfy the maximum values that are contained in each connection setup message. However, if a parameter is additive, such as transmission delay or jitter, such local verification does not make it possible to ensure that the parameter will be satisfied from one end of the connection to the other. Each node on a connection path can individually and locally satisfy some maximum value, but if the local values of an additive parameter as added by the various nodes along the connection path accumulate, then the maximum value can end up being exceeded.
Consequently, although the above-presented integration does indeed enable maximum values to be transmitted to the nodes along a connection path, the way in which the maximum values are used and the read-only restriction that is imposed on the objects of the SENDER_TSPEC attribute, mean that it is not possible to guarantee that the connection does in fact comply with the maximum parameter value(s) once it has been set up.